Abstract: As China steel industry continues to face more prominent overcapacity and environmental pollution problems, reduction of ferroalloy continues to attract more attention as a cost reduction and efficiency improvement method. In this paper, the current research status of ferroalloy reduction was summarized. Advancements on ferroalloy reduction were discussed from three aspects:ferroalloy physical and chemical characteristics, ferroalloy addition technique, and steelmaking process. The control technique of ferroalloy self-powdering, loss encountered under vacuum conditions during ferroalloy utilization, melting of ferroalloy in molten steel, and alternative techniques were introduced. These techniques can serve as a reference for ferroalloy reduction during steelmaking. The shape, physical, and chemical properties as well as complex structure affect the yield of ferroalloy during steelmaking. The manner of ferroalloy addition, sequence and time of ferroalloy addition were summarized and contrasted. Self-powdering and bitterness-powdering of ferroalloys are difficult problems during the utilization of these alloys, and should be controlled at the initial usage of ferroalloys. Powdered and volatile ferroalloys easily encounter loses under vacuum conditions, and better utilization can be realized by lowering the vacuum conditions, as it can lead to a low flow speed of the argon in the vacuum chamber and reduce the volatility rate of the elements in volatile ferroalloys. In addition, ferroalloys with different densities and granularities have different melting time and movement tracks. Large ferroalloys with a low density have a long melting time and easily float between molten steel and slag, which can cause ferroalloy oxidation. Therefore, the yields obtained using ferroalloys with different densities and granularities are different. Ferroalloys of different structures and granularities should be designed to optimize yields. The application of ferroalloy reduction techniques has extensive prospect. Investigation of the mechanism of ferroalloy loss, structural design of ferroalloys, as well as alternative techniques and control techniques should be key research areas in ferroalloy reduction during steelmaking.
Abstract: In cement production, the synergistic use of municipal solid waste incineration (MSWI) fly ash provides a novel approach to solve the problem of the increasing productions of fly ash and heavy metal ions. In this study, slag-steel slag based cementitious material (referred to as metallurgical slag cementitious materials) was combined with four types of MSWI fly ash for preparing cementitious materials, all of which use sand as a binder. According to the determination of fluidity, compressive strength and Cd2+ leaching concentration of filler samples, the following are found:(1) the flow rate of filler material prepared from metallurgical slag and fly ash is 240-265 mm, which fulfills the pumping requirement of mine filling; (2) the 28-day compressive strength values are>8.88 MPa, which meets the general mine filling strength requirements (1-6.5 MPa); and (3) the Cd2+ leachate concentration is lower than the drinking water standard of 5 μg·L-1 limit. The results of X-ray diffraction, infrared spectroscopy, and thermogravimetry-differential scanning calorimetry show that the leading hydration products of gelling materials are ettringite, Friedel, and C-S-H. Furthermore, X-ray photoelectron spectroscopy results reveal that Cd2+ has a great effect on the binding energy of Al3+. Ettringite and Friedel salts are found to have a curing effect on cadmium ions.
Abstract: Pyrite cinder is one of the important secondary resources; however, the arsenic typically contained in pyrite cinder is harmful to metallurgical process. The removal of arsenic can improve the value of pyrite cinders. Thus, a pretreatment method for removal of arsenic from pyrite cinders using a Na2S-NaOH solution was investigated in this paper. A single factor experiment was conducted to determine the appropriate concentration ranges of NaOH and Na2S, and then the response surface methodology (RSM) was used to optimize the leaching parameters. The results indicate that the optimized RSM model is reliable. The temperature, NaOH concentration, and Na2S concentration have significant effects on the arsenic removal. The higher temperature is found to be favorable to the leaching of arsenic, and a significant interaction is found between the concentrations of NaOH and Na2S. The content of arsenic in the leaching slag can be reduced to 0.08% at 80℃ when the concentration of NaOH and Na2S is 0.34 and 0.12 mol·L-1, respectively.
Abstract: The strength, deformability, and flow properties of rock discontinuities are strongly affected by the surface characteristics. Therefore, a quantitative description of the topography of the discontinuities is very important. The projective covering method (PCM) is useful in calculating the fractal dimensions to measure the irregularity and roughness of fracture surfaces. However, there is a defect in the division of a grid cell into two triangles, which is, for every grid cell, only one dividing scheme is used to calculate the fractal dimensions with the projective covering method, despite the availability of two schemes. Moreover, it has been confirmed that when a small grid cell is divided by a different triangulation division scheme, differing fractal dimensions are calculated. To obtain a grid cell division method whose result is consistent with the surface morphology of the studied fracture surface, which comprises thousands of grid cells, improved projective covering method (IPCM) was propose based on stochastic analysis. In this method, a random number was generated by the random function and its parity was judged. If the number was odd, the small grid cell was divided using one scheme. Otherwise, it was divided by the other scheme. With this method, the fractal dimensions of the discontinuity of a redsandstone was calculated and 120 fractal dimensions were obtained, which formed a sample space. Secondly, the distribution characteristics of the sample space was determined, and the average of the sample was regarded as the accurate fractal dimensions of the redsandstone discontinuity. The analysis shows that the sample of fractal dimensions follows a normal distribution, the calculated results by the projective covering method are the maximum or minimum values of the fractal dimensions estimation, and because the result of the dividing scheme using stochastic analysis method is more consistent with the surface morphology, the fractal dimensions obtained by improved projective covering method are more accurate.
Abstract: Integrated optimization of production plays a key role in realizing short completion times of underground mine processes. To achieve the best production operation, a production plan should consider factors such as the working time and equipment capacity to arrange stope mining operations, equipment, and materials supply. Underground mining operation is a process with multiple working sites and multiple cycle operations, which include rock drilling, blasting, ventilation, supporting, ore-transportation, and backfilling. Once the stope mining begins, the above six steps must be intensively integrated to minimize the exposure time. Each step of stope mining has a significant effect on the whole mining plan; therefore, it is very important to form a reasonable configuration to achieve the mining plan target. The most difficult part of underground mining operation is how to organize the production process with limited resources (i. e., equipment and materials) to accomplish a large production task. In this paper, an integrated optimization model was described for compacting the integrated production process and efficiently dispatching production equipment. Two optimal objectives were combined to shorten the interval between production processes and overall working time. Production factors such as production cycle, type of operation equipment, and production capacity are analyzed in a mathematical model. In addition, the production safety was also considered and the time intervals between different working processes were considered to shorten the stope uncontrolled time to keep the production safety in the mathematical model. The best result of mining sequence and equipment dispatching was obtained by an improved genetic algorithm which searches the feasible solutions through primary-secondary two-step searching method. The model was validated in a large gold mine in China to work out the optimal equipment scheduling plan. The results show that compared with the traditional single-target optimization, the mining task can be accomplished effectively and the intervals between processes are minimized to improve safety in the mining operation.
The adverse effects of harmful elements on blast furnace life and production have been adequately researched; however, studies of the effects on the energy consumption of blast furnace are few. In this study, the circulation and accumulation of harmful elements in a blast furnace were analyzed. By combining the actual production parameters of a blast furnace and the Rist operating diagram, the effect of the harmful elements on the coke ratio was revealed and the quantitative relationship between the coke ratio and the loads and accumulation times of harmful elements was established. The calculation results show that the harmful elements cycle of "reduction-oxidation-re-reduction" in the blast furnace can transfer the CO from the high-temperature zone to the low-temperature zone, and consume a lot of heat in the high-temperature zone. This can decrease gas utilization and increase heat consumption in the hightemperature zone, consequently increasing the coke ratio. Each harmful element affects the coke ratio differently. Considering their accumulation times and loads, the harmful elements affect the coke ratio in the following orders:Na > K > Zn and Zn > Na > K, respectively. Further analysis shows that the effect of Na and Zn on the coke ratio is greater than that of K. However, considering the effect of K on coke deterioration is more significant, it is necessary to strictly control the load of K, Na, and Zn. Based on the quantitative relationship obtained by the above calculation process, curve fitting is carried out using the loads of harmful elements and coke ratio of blast furnace to predict the harmful elements accumulation times in the blast furnace. The curve fitting results are consistent with the blast furnace dissection experiment results.
Abstract: Ultralow-carbon (ULC) steel slabs are usually used for manufacturing high surface quality products such as automobile panel. Severe hooks in the subsurfaces of ultralow-carbon steel slabs usually degrade the surface quality of slab because of inclusions entrapment, which results in unacceptable sliver and blister defects on the surface of the final cold-rolled strip products. The hook formation and evolution process during the initial solidification of a continuous casting slab were studied through numerical modelling. A physical model based on the numerical simulation results was constructed to simulate the process of inclusion entrapment near the hook region, and the forces of inclusions in different positions of the solidified hook region were analyzed. The results demonstrate that following formation, the hook is not immediately buried in the shell; it sustained several stages such as melting, coarsening, growing, and burying. It is predicted that the final hook depth, as buried in the shell, is 2.5 mm when the casting speed is 1.3 m·min-1, which is basically the same as the actual size of the hooked shell observed by a metallographic experiment. The calculated shape of the shell inner face with hooks is similar to morphologies of the slab surface region and breakout shell. The results of physical simulation and force analysis show that inclusions are most likely to be caught by the lower face of the solidified hooks, but they are more difficult to be entrapped by the upper face of the hook, especially for large-size inclusions. However, when overflow occurs, the inclusions near the me-niscus may be wrapped by the rapidly cooled molten steel above the primary hook. In the vertical shell between the two adjacent hooks, small-size inclusions (less than 100 μm) may be wrapped by the solidified front, but large-size inclusions are difficult to be wrapped.
Abstract: In this study, an Al-Mg-Si-Cu alloy was prepared by conventional press-and-sinter powder metallurgy techniques using pure Al powder, Cu element powder, and binary Al-Mg and Al-Si powders to investigate the processes of atom diffusion and microstructure evolution. The relative density of the sintering samples exceeded 98%. It is found that the sintering densification process can be approximately divided into three stages. In the first stage (from room temperature to 460℃), after the Al-Mg eutectic liquid phase formed at 450℃, the Mg atoms in the liquid diffuses into Al and Al-Si particles and reacts with Al2O3 at the metal/oxide interface to form an Al-Mg-O compound. Meanwhile, the interdiffusion between Al and Cu leads to the formation of Al2Cu compounds. In the second stage (from 460 to 560℃), the micro-channels or small holes between the grain boundaries are rapidly filled by Al-Cu and Al-Si eutectic liquids, which leads to a significant increase of density. In this stage, the densification mechanisms are particle rearrangement controlled by the capillary driving force and contact flattening dominated by solution-reprecipitation. In the last stage (from 560 to 600℃), the residual large holes are finally filled by the liquid because of the enhancement of wettability and grain growth with the increase of sintering temperature. In this stage, the densification mechanism is mainly pore-filling, resulting from the grain growth. The sample is fully dense through this stage. In addition, MgAl2O4 and MgAlCuO compounds are found in the grain boundary region; thus, it can be speculated that the mechanism of oxide film disruption is related to the alloy composition. Furthermore, because of the good wettability between Al-Cu liquid and Al, the surface of Al particles is quickly wetted by the liquid under the capillary driving force; therefore, no AlN is found in the grain boundary region in this research.
Abstract: The tensile test of an ultra-high strength hot stamping steel was tested using the CMT5105 electronic universal testing machine and HTM 16020 electro-hydraulic servo high-speed material testing machine. The impacts of the hot stamping parts were simulated at strain rates range of 10-3-103 s-1. The results show that in the low strain rate (10-3-10-1 s-1), the strain rate sensitivity of the tested steel is not very high, and the steel strength and elongation change little with an increase of strain rate. In the high strain rate stage (100-103 s-1), the strain rate sensitivity of the steel is very high, and the steel strength and elongation increase with strain rate. The strain rate sensitivity of the tensile strength is higher than the yield strength mainly because of the adiabatic temperature rise phenomenon and the strain working phenomenon that simultaneously occur during the high strain rate stage. The elongation after necking decreases with an increase of strain rate, mainly because of the local inhomogeneous deformation of the martensite at the high strain rate. The impact energy absorption capacity of the experimental steel increases with strain rate, and is more sensitive at the uniform elongation. Compared with the low strain rate stage, the average fracture diameter of the dimple in the high strain rate stage is smaller, and its depth is deeper; this is related to the fragmentation of the martensite grains region in the high strain rate stage. Scanning elec-tron microscope and transmission electron microscope images reveal that the grains are elongated at high strain rate stage and some microvoids are present in the stress-concentrated regions. Moreover, the fragmentation phenomenon can be found in part of region at the 103 s-1 strain rate.
Abstract: With the continuous petroleum extraction from deep-water subsea gas fields, many long distance offshore natural gas pipelines have been constructed. The design parameters directly affect the gas flow velocity in pipelines, which may introduce high wall shear stresses on the pipeline internal wall. Moreover, corrosive medium like CO2, H2S, O2, and Cl- always exists in subsea pipelines under high velocity gas flow, which induces erosion-corrosion. Many pipelines in China have entered the middle or late stage of service, and this has increased the risks and failures induced by erosion-corrosion. Furthermore, more natural gas storages are being built for transportation, which require a high-velocity gas flow for gas injection and production processes. A certain amount of corrosive mediums such as residual drilling fluid, hydrochloric acid, condensate water, CO2, and H2S can be found in natural gas, and when combined with a high gas flow velocity, internal erosion-corrosion might occur in the tubing in downhole systems. In this study, a high temperature-high pressure flow loop was applied to investigate the corrosion behavior of L80 steel in a wet gas pipeline with a high gas velocity. The extreme conditions created by the flow loop is 30 m·s-1 gas velocity, 0.0007% water cut, 0.5 MPa CO2 partial pressure, and 55℃ environmental temperature. Corrosion rates at different testing periods were calculated through weight-loss measurements. Confocal laser scanning microscopy and scanning electron microscopy were applied to observe the corrosion morphology. The corrosion product constituents were analyzed using X ray diffraction and energy dispersive spectroscopy (EDS), and the results reveal that severe corrosion occurs and a large number of micro pits appear on the L80 coupons surfaces. Moreover, instead of an integral corrosion prod-uct film, FeCO3 corrosion product chips and Fe3C are present on the steel.
Abstract: Hydrogen dew point corrosion often occurs in the overhead condensing and cooling system of an atmospheric distillation unit at the initial process of petroleum refining because of the formation of a highly suitable corrosive environment. The consequent thinning and leakage of equipment cause serious environmental pollution and endanger personal safety. Hydrochloric dew point corrosion is affected by various factors, among which temperature and pH values are the most critical. In this study, the hydrochloric dew point corrosion behavior of the 20# steel of an atmospheric tower overhead system as well as its corrosion rate, corrosion morphology, and corrosion products at different temperatures and pH values were analyzed by some analytical methods, such as weight loss method, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The results indicate that the hydrochloric dew point corrosion rate of the 20# steel first increases and then decreases with temperature increase, and reaches its peak at 90℃. The hydrochloric acid dew point corrosion rate of the 20# steel is negatively correlated with the pH values of HCl solution, and the dew point corrosion rate decreases rapidly with an increase of the pH value of HCl solution. Generally, uniform corrosion occurs on the steel surface accompanied with local corrosion pits. When the temperature is higher than 90℃, the number of corrosion pits increases with temperature. The corrosion pits become shallower and decreases with an increase of pH value. In addition, the chloride ions in the solution deepen the pits and accelerate the corrosion. The XRD analysis shows that the main compositions of the corrosion products are α-FeOOH, Fe3O4, and γ-FeOOH.
Abstract: The kinetics and mechanical properties of borided GCr15 bearing steel was investigated. The boriding treatment was carried out in a solid medium at 1123, 1173, 1223, and 1323 K for 2, 4, 6, and 8 h. The microstructures and mechanical properties of the boride layer were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, and Vickers hardness tester, and the growth kinetics characteristics were also studied based on experimental data. The results indicate that the boride layer has a smooth and compact morphology, and the presence of FeB and Fe2B on the steel substrate is confirmed by X-ray diffraction analysis. The thickness and hardness of the boride layer increase with treatment time and temperature, where the thickness ranges from 33.4 to 318.5 μm. The increased hardness is mainly because of the increase in the highly hard FeB phase content. The content of Fe2B phase, which has a low hardness, decreases with an increase of layer thickness. The hardness of the boride layer HV0.1 ranges within 1630-1950, and it is increased by 5 to 6 times compared with the matrix. The hardness test results of the boride layer cross section indicate that there is a wide transition of hardness gradient between the boride layer and the matrix. The kinetic equation based on the experimental data and Arrhenius equation was investigated, the active energy of B element in the GCr15 bearing steel is 188.595 kJ·mol-1, and the derived kinetic equation is verified by experiments. The results indicate that the maximum error between the theoretical derivation and experimental derivation is 4.93%. Therefore, the derived kinetic equation can effectively predict the thickness of the boride layer on GCr15 bearing steel.
Abstract: At present, the traditional insulated pole electroscope is used for electrical inspection in high-voltage transmission lines. However, when it is used in ultra-high voltage (UHV) transmission lines, the length of its insulated rod is large, and there are disadvantages such as large working intensity, inconvenience, and hazardous operation. In this study, an electroluminescent inorganic material was made to be used for inspection mark. The material was placed around the wire, so that it glowed during the electric fielddriven movement of electrons to promote carrier recombination, through which the charged situation could be determined. Therefore, the electrification of the line can be judged through the material luminescent properties, making it very convenient to be used for inspection mark. In this study, GaN materials were investigated. Based on the GaN, InGaN, and other materials, the contact layer, substrate layer, material layer and other structures were made by methods such as sol-gel method and gas phase epitaxy. Then the inspection mark was prepared. The light-emitting layer was a nanorod array with a multi-quantum hydrazine structure. The electrical and optical properties of the inspection mark were tested, and the relevant characteristic curve was obtained. Through a simulation of the Ansoft-maxwell finite element software, the electric field distribution of the inspection mark and surrounding transmission lines were analyzed. Through experiments, the electromagnetic environment needed for electroluminescence was tested in the high-voltage test hall of Wuhan University. Finally, the inspection mark was tested in a working environment simulated in the Feng-huang ultra-high voltage test site. The research shows that the low-field electroluminescent inspection mark has the advantages of low power consumption and obvious luminescence. When it is in an area where the electric field strength is above 1.2×106V·m-1, the light can be excited and the injected current is about 1.1 mA. Simulation and experimental analysis show that the electric field strength around the UHV transmission lines meets the requirements of the light-emitting indication of an electroscope. Meanwhile, the space stray current and capacitance effect of the material provide the injection current. The inspection mark indicates the charged state through the light-emitting properties. Its installation can be within a distance of 13 cm from the UHV conductor axis, and it has good weather resistance. Meanwhile, it avoids problems such as electromagnetic interference and poor reliability that occur in electroscope equipment with complex circuits.
Abstract: During welding processes, initial defects such as incomplete penetration and slag are easily generated. To ensure the safe operation of welding components, welded joints must be tested rigorously. Metal magnetic memory (MMM) technology, a new nondestructive testing in the 21st century, can detect macroscopic defects as well as early stress concentrations and hidden damages. However, the quantitative MMM testing is still a bottleneck for weld defects. To solve the bottleneck of quantitative inversion of weld defects by MMM testing, a quantitative inversion model was presented based on a support vector machine (SVM) method optimized with simulated annealing (SA) algorithm. Steel Q235 welded plate specimens, which were prefabricated with different sizes of incomplete penetration and slag defects, were tested. It is found that with the increase of weld damage degree, the peak-peak values of the tangential and normal magnetic field intensity exhibit nonlinear growth, as well as the change rates of the tangent and normal magnetic field intensity. In other words, the MMM feature parameters vary with the defect size, but the signals are scattered and uncertain. First, considering the finite, dispersive, and non-linear MMM signals, the MMM feature parameters data were normalized, and the MMM quantitative inversion model of weld defects was established based on SVM. Furthermore, the SVM parameters was optimized with SA so that the objective function of the model could reach the global optimal solution. Finally, considering the solution uncertainty when the three-dimensional sizes of weld defects were reversed from the MMM signals, a modified MMM multi-dimensional SVM inversion model was presented by constructing SVM multi-layer structures and optimized with SA. The results show that maximum inversion relative error of incomplete penetration defect size is 7.96%, and the defect of slag is 4.97%, which provides a new tool for quantitative MMM inversion and evaluation of weld defects.
Abstract: Contact strain measurement is used to study the high-temperature mechanical behavior of materials and components. The measurement precision, which is mainly affected by the thermal output, is very vital in high-temperature strain measurement. By combining experimental analysis with the theories of materials physics, elastic mechanics, thermos-dynamics, mechanical engineering testing technology, and finite element method (FEM), the influence factors of the thermal output error of high-temperature strain gauge were studied, and a compensation model was established, and then a test was conducted to verify the model accuracy and experimental results. In this study, the coupling characteristics of the thermal output of high-temperature strain gauges were investigated based on the thermal expansion theory and the temperature-resistance properties of the material, and the thermal output model of strain gauges was established. Then, the theoretical expression of the heat output under the coupled action of the member, rubber layer, and strain gauge was obtained. Based on the resistor-temperature effects, the electrical conductivities of different wire materials were obtained, and the thermal output property of the grid wire was studied by finite element method. According to the results, two kinds of wire mesh materials were selected as the research object of this paper, and the simulation results were compared with the experimental data, the relative error is less than 7%. Finally, a compensation model of high-temperature strain thermal output was obtained from the theoretical model and experimental results. The results show that the error between the compensation correction and the theoretical value is less than 9%; thus, the error compensation is efficient.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
